#version 330 core
struct Material{
  sampler2D diffuse;
  sampler2D specular;
  float shininess;
};


struct Light{
  vec3 position;//固定点光源
  //vec3 direction;//定向光源

  vec3 ambient;
  vec3 diffuse;
  vec3 specular;

  //光照衰减用三变量
  float constant;
  float linear;
  float quadratic;
};

out vec4 FragColor;
in vec2 TexCoords;

uniform Material material;
uniform Light light;
uniform vec3 viewPos;

in vec3 Normal;
in vec3 FragPos;


void main()
{
  //ambient
  vec3 ambient = light.ambient * vec3(texture2D(material.diffuse, TexCoords));

  //diffuse
  vec3 norm = normalize(Normal);
  vec3 lightDir = normalize(light.position - FragPos);//固定点光源
  //vec3 lightDir = normalize(-light.direction);//定向平行光源
  float diff = max(dot(norm, lightDir), 0.0f);
  vec3 diffuse = light.diffuse * (diff * vec3(texture2D(material.diffuse, TexCoords)));

  //specular
  vec3 viewDir = normalize(viewPos - FragPos);
  vec3 reflectDir = reflect(-lightDir, norm);
  float spec = pow(max(dot(viewDir, reflectDir), 0.0f), material.shininess);
  vec3 specular = light.specular * (spec * vec3(texture2D(material.specular, TexCoords)));

  //光照衰减公式
  float distance = length(light.position - FragPos);
  float attenuation = 1.0 / (light.constant + light.linear * distance + light.quadratic * (distance * distance));

  //all
  vec3 result =  (ambient + diffuse + specular) * attenuation;
  FragColor = vec4(result, 1.0f);
}
